User blog comment:Andreiva13/Natures/@comment-31267872-20170730160020

It depends on the Pokémon for which nature is the best. Each Pokémon has a nature, and a nature raises one stat and lowers one stat. For example, I believe the Quiet nature raises Sp. Attack but lowers Speed. Hardy raises Attack and yet lowers Attack at the same time... some natures are like that.

It depends on which stat the Pokémon is best in that determines which nature is best for that Pokémon. Of course, natures aren't influenced by how good a stat is - natures influence how good a stat is.